OF THE VERTEBRAL COLUMN. 225 



front to the anterior, and behind to the posterior common ligament ; whilst in the 

 dorsal region they are connected laterally, by means of the interarticular ligament, 

 to the heads of those ribs which articulate with two vertebrae ; they, consequently, 

 form part of the articular cavities in which the heads of these bones are received. 

 Structure of the Intervertebral Substance. The intervertebral substance is 

 composed, at its circumference, of laminae of fibrous tissue and fibro-cartilage ; 

 and, at its centre, of a soft, pulpy, highly elastic substance, of a yellowish color, 

 which rises up considerably above the surrounding level when the disk is divided 

 horizontally. This pulpy substance, which is especially well developed in the 

 lumbar region, is the remains of the chorda dorsalis, and, according to Luschka, 

 contains a small synovia! cavity in its centre. The laminae are arranged concen- 

 trically one within the other, the outermost consisting of ordinary fibrous tissue, 

 but the others and more numerous consisting of white fibro-cartilage. These 

 plates are not quite vertical in their direction, those near the circumference being 

 curved outward and closely approximated ; whilst those nearest the centre curve 

 in the opposite direction, and are somewhat more widely separated. The fibres of 

 which each plate is composed are directed, for the most part, obliquely from above 

 downward, the fibres of adjacent plates passing in opposite directions and varying 

 in every layer ; so that the fibres of one layer are directed across those of another, 

 like the limbs of the letter X. This laminar arrangement belongs to about the 

 outer half of each disk. The pulpy substance presents no concentric arrangement, 

 and consists of a fine fibrous matrix, containing angular cells, united to form a 

 reticular structure. 



2. LIGAMENTS CONNECTING THE LAMINAE. 

 Ligamenta Subflava. 



The Ligamenta Subflava (Fig. 152) are interposed between the laminae of the 

 vertebrae, from the axis to the sacrum. They are most distinct when seen from 

 the interior of the spinal canal ; when viewed from the outer surface they appear 

 short, being overlapped by the laminae. Each ligament consists of two lateral 

 portions, which commence on each side at the root of either articular process, and 

 pass backward to the point where the laminae converge to form the spinous 

 process, where their margins are in contact and to a certain extent united ; slight 

 intervals being left for the passage of small vessels. These ligaments consist of 

 yellow elastic tissue, the fibres of which, almost perpendicular in direction, are 

 attached to the anterior surface of the laminae above, some distance from its 

 inferior margin, and to the posterior surface, as well as to the margin of the 

 lamina below. In the cervical region they are thin in texture, but very broad and 

 long ; they become thicker in the dorsal region, and in the lumbar acquire very 

 considerable thickness. Their highly elastic property serves to preserve the 

 upright posture and to assist in resuming it after the spine has been flexed. 

 These ligaments do not exist between the occiput and atlas or between the atlas 

 and axis. 



3. LIGAMENTS CONNECTING THE ARTICULAR PROCESSES. 

 Capsular. 



The Capsular Ligaments (Fig. 154) are thin and loose ligamentous sacs, attached 

 to the contiguous margins of the articulating processes of each vertebra through 

 the greater part of their circumference, and completed internally by the ligamenta 

 subflava. They are longer and looser in the cervical than in the dorsal or lumbar 

 regions. The capsular ligaments are lined on their inner surface by synovial 

 membrane. 



4. LIGAMENTS CONNECTING THE SPINOUS PROCESSES. 



Supraspinous. Interspinous. 



The Supraspinous Ligament (Fig. 152) is a strong fibrous cord, which connects 



is 



